The present invention relates generally to initiators for use with perforating charges, such as are used in oil and gas wells; and more specifically relates to high temperature initiators for use with high temperature explosives in capsule charges suitable for use in down hole perforating guns.
Capsule type charges are generally capable of superior performance when compared to the equivalent charge shot in a thru-tubing gun. Capsule charges are well known in the art of well bore perforation. Typical capsule charge designs are illustrated in U.S. Pat. Nos. 3,128,702; 2,734,456; and 3,048,102, which are hereby incorporated by reference. In each instance, the capsule charge denotes a fully sealed or encapsulated shaped charge. A plurality of capsule charges are typically suspended on a charge carrier comprised of metal wire or strips. The use of these types of charge carriers is often selected to permit the carrier holding the capsule charges to be passed through a restricted opening in the well bore. The carrier then expands to properly position the charges.
In order to be effective, the charges must be fully encapsulated to prevent exposure of the primary explosive to well bore fluids and pressures. This requires that the capsule charges be detonated by a means external to the sealed capsule. This is typically accomplished by means of a detonating cord positioned adjacent to the rear of the charge capsule. See, for example, U.S. Pat. No. 4,739,839, which is hereby incorporated by reference, having capsule charge 24 and a detent at the rear 56 designed to receive detonating cord 26. However, there are problems encountered when attempting to use capsule charges in high temperature environments (i.e., in excess of +350 F.). Namely, the commercially available high temperature explosives are not sensitive enough to be initiated across the steel barrier which is necessary to maintain the charges integrity under pressure.
Therefore, what is needed is an initiator that works well with capsule charges at high temperatures.